Process of and apparatus for drawing glass



Dec. 13, 1955 E. BRICHARD PROCESS OF AND APPARATUS FOR DRAWING GLASSOriginal Filed Aug. 4, 1949 IN VENTOR EDGARD BR/CHARD ATTORNEY UnitedStates Patent Otlce 2,726,486 Patented Dec. 13, 1955 PROCESS F ANDAPPARATUS FOR DRAWING GLASS Edgard Brichard, Jumet, Belgium, assignor toUnion des Verreries Mecaniques Belges S. A., Charleroi, Belgium, acompany of Belgium Original application August 4, 1949, Serial No.108,452, now Patent No. 2,693,052, dated November 2, 1954. Divided andthis application September 17, 1954, Serial N o. 456,789

Claims priority, application Belgium May 17, 1949 5 Claims. (Cl. 49--17)This invention relates to the vertical drawing of sheet glass from abath of molten glass and is directed to the provision of a process andapparatus for producing drawn glass in sheet form of generally improvedappearance.

This application is a division of my copending application Serial No.108,452, led August 4, 1949, now Patent No. 2,693,052. f

It is known that movement of relatively cold air along and in contactwith the surfaces of the glass sheet while they still remain plastic,and with surfaces of the bulb that normally forms at the foot of theglass sheet as it is drawn from the molten glass bath, producesmodifications in the characteristics of the glass which impair the finalappearance of the glass surface.

In the drawing of sheet glass by the vertical drawing process a zone ofreduced pressure tends to forrn in the gaseous atmosphere surroundingthe foot of the freshly formed glass sheet and the adjacent bulbsurfaces. This is due to the fact that the gases coming in contact withthe hot sheet of glass are heated thereby and rise along both faces ofthe glass sheet. The upward flow is also aided by movement of the glasssheet. As a result of the above action relatively cool gases present inthe portions of the drawing chamber that are more remote from the bulband the highly heated surfaces of the glass sheet are caused to flowtowards the bulb and the foot of the glass sheet. from the outsidethrough cracks and access openings which cannot be entirely sealed.Usually coolers are also positioned at the opposite sides of theascending glass 'sheet to absorb heat radiated therefrom and promotesolidifying of the glass sheet. These coolers also set up convectioncurrents in the gaseous atmosphere surrounding them with the result thata relatively cool air current may move from the vicinity of the coolerstoward the zone of reduced pressure adjacent the foot of the glasssheet. Due to the thermosiphoning action above described, the relativelycold air and gases are drawn inwardly towards the bulb and tend to comeinto contact with the bulb and the portions of the glass sheet adjacentthe bulb while the glass sheet is still in a plastic form with theresult that undesirable striations are formed in the surfaces of thefinished sheet and other harmful effects are produced.

The problem is one peculiar to the vertical drawing of the glass ascontrasted to horizontal drawing since only in the former process is theglass sheet drawn upwardly from the drawing chamber through a longvertically eX- tending leer in communication therewith, and which,because of its vertical extent and direct communication with the drawingchamber, creates a chimney or draft effect along the sides of the newlyformed glass sheet. In contrast, in the horizontal process the glasssheet is bent over a roller while still plastic. The contact with theroller alters the sheet far more than air currents would do, andconsequently the horizontal process does not lend In addition cold airenters the drawing chamberA itself to the production of sheet glasshaving a high degree of freedom from surface imperfections. In thehorizontal process the drawing chamber is generally open at both endswith no attempt made to control the inlet of cold air.k This is inmarked contrast to the vertical drawing process wherein it is sought toeliminate as far as possible the entry of any air from outside thedrawing chamber and to avoid contact of cold air with the surfaces ofthe glass sheet while they remain plastic.

Efforts have been made to deect these harmful relatively cold aircurrents by producing other currents whose eiect on the sheet is lessharmful but the results of such measures as heretofore proposed havenever been perfect since harmful currents of ar always remain in thevicinity of the bulb and the adjacent plastic surfaces of the freshlyformed glass sheet. An attempt has also been made to protect the sheetfrom the harmful currents by means of barriers but for operationalpurposes it is impossible to make such barriers continuous with theresult that the inuX of air currents is concentrated at the gaps in thebarriers which increases the harmful effects at these particular points.

The present invention has for an object to produce sheet glass by thevertical drawing process that is free from surface striations and has agenerally improved surface appearance.

It is a further object of the invention to prevent harmful currents ofair from coming into contact with the bulb and the adjacent plasticsurfaces of the glass sheet.

It is a still further object to reduce the amount of heat required to besupplied to the glass bath to maintain a satisfactory drawing operation.

According to the present invention harmful currents of air are preventedfrom coming into contact with the bulb and the adjacent plastic surfacesof the glass sheet by altering the normal pressure relationships in thedrawing chamber. More specilically, l have found that the tendency forcold air currents to be brought into contact with the bulb and adjacentplastic surfaces of the glass sheet can be overcome by bringing about areduction in the pressure of the atmosphere present in the drawingchamber in zones thereof spaced laterally with respect to the bulb andthe glass sheet and adjacent the bath surface at least sucient tobalance any reduction in the pressure in the inner zone immediatelyadjacent the bulb and the base of the sheet caused by the tendency ofthe gases in contact therewith and immediately adjacent thereto to 'riseas they become heated. Preferably the reduction of the pressure in thelaterally spaced zones will be somewhat greater than the pressurereduction in the zones irnmediately adjacent the bulb and the adjoiningportions of the glass sheet so that the normal tendency for an upwardflow of air in contact with the side surfaces of the rising sheet ofglass will be reversed.

As more particularly hereinafter described, I bring about the desiredreduction in pressure by providing suitably apertured conduits or pipesextending along the sides of the glass sheet in laterally spacedrelation theretov and at a level adjacent but spaced from the surfacesof the molten glass bath vand applying suction thereto throughconnection of the pipes with an appropriate suction means.

The invention will be more fully understood by reference to thedrawings, the accompanying detailed description and the appended claims.

In the drawings:

Fig. l is a vertical section taken along line 1--1 of Fig. 2; and

Fig. 2 is a horizontal section taken alone line 2 2l of Fig. l.

The invention is shown by way of example as being carried out with theuse of a sheet forming block or debiteuse which is located Aat thesurface -of the glass bath; that is to say, as applied to the practiceknown in the art as the Foucault process. However, it will be readilyappreciated that .the invention is equally applicable to the Pittsburghprocess wherein the glass is drawn into a sheet with the use of asubmerged draw bar.

The drawing chamber Sis insulated from the furnace atmosphere 6 by apartition 7 of a refractory material. The other side wall 8 of thechamber forms the end wall of the furnace. A pair of refractory elements9 tend to isolate the drawing chamber proper from the superimposedvertically extending cooling chamber or leer 10.

The glass sheet 11 is formed from the bath of molten glass 12 through aforming bulb 13 defined within a drawing frame or block 14 of refractorymaterial positioned in the drawing chamber. The glass sheet 11 is drawnupwardly through the vertical chamber by a series of rollers 16 whichare positioned at a point along the sheet where it has become solid.Cooling tubes 17 are shown on both sides of the sheet at points spacedabove the draw ing block and outwardly from the sheet for absorbing heatradiating from the glass sheet and accelerating the cooling thereof tothe solid state.

A pipe 18 is positioned along each side of the sheet near the level ofthe bulb but spaced laterally therefrom and generally parallel thereto.A pair of end pipes 19 are similarly spaced from the ends of the bulb.All the pipes 18 and 19 have small openings that extend along the lengthof the pipe. These may be individual spaced apertures 21 as shown in thedrawings or may consist of a narrow slot or slots. As shown only on oneend of Fig. 2, screens 22 may be provided adjacent the ends of the glasssheet to avoid setting up of conflicting air currents in this area.

The pipes 18 and 19 are connected to an external source of suction, notshown. If desired, the air, or other gases removed in this manner may bereturned to some portion of the drawing chamber or the cooling chamberwhere contact with the drawn glass sheet will not be harmful. The endpipes 19 may be omitted without greatly reducing the desired effectssince only a relatively small surface area of the glass sheet isaffected thereby.

Suicient suction is applied through the pipes 18 and 19 so that thepressure of the gaseous atmosphere in the immediate vicinity of thepipes will be at least as low as the pressure immediately adjacent thebase of the bulb and will, therefore, cause the air from the base of thebulb to move laterally toward and into the suction pipes. This in turnwill cause a current of air to move downwardly along each surface of theglass sheet as shown by the arrows in Fig. l. The movement of this hotair downwardly along the sheet does not in any way impair the surface ofthe sheet.

Although it is preferable to create enough suction in the pipes so thatthe normal upwardly-moving air currents along the surface of the sheetare reversed, it is sufficient if the lowered pressure at the suctionpipes is just enough to eliminate the entry of cold air into the zoneimmediately adjacent the base of the glass sheet around the bulb. Inother words, rising warm air currents or the absence of air currentsdoes not impair the surface of the sheet.

I claim:

l. A process for the vertical drawing of glass in sheet form from aheated bath of molten glass including drawing the glass from the surfaceof the bath upwardly through a drawing chamber immediately above saidbath and simultaneously withdrawing air from said drawing chamber atpoints adjacent the bath surface and spaced from the base of the glasssheet at a rate sufficient to maintain the pressure in an outer zoneadjacent said points at least as low as the pressure in an inner zoneimmediately adjacent the base of the sheet to prevent air currentsflowing toward said inner zone from said outer zone, said zones being inopen communication.

2. A process for the vertical-drawing of glass in sheet form from aheated bath of molten glass including drawing the glass from the surfaceof the bath upwardly through a drawingchamber immediately above saidbath and simultaneously withdrawing air from said drawing chamber atpoints adjacent the bath surface and spaced from the base of the glasssheet `at a rate sufficient to reduce the pressure in an outer zoneadjacent said points of withdrawal below the pressure in an inner zoneimmediately adjacent the base of the sheet, said zones being in opencommunication so that the difference in the pressures tends to produceair currents flowing from said inner zone toward said outer zone.

3. A process for the vertical drawing of glass in sheet r'orm from aheated bath of molten glass including drawing the glass from the surfaceof the bath upwardly through a drawing chamber immediately above saidbath and simultaneously withdrawing air from said drawing chamber atpoints just above the bath surface and spaced from the base of the glasssheet along both sides and both ends of said sheet, said air withdrawalbeing at a rate suicient to reduce the pressure in an outer zoneadjacent said points below the pressure in an inner zone immediatelyadjacent the base of the sheet, said zones being in open communicationso that the diiference in pressure tends to produce air currents flowingaway from said inner zone toward said outer zone.

4. Apparatus for drawing glass in sheet form from a heated bath ofmolten glass comprising a drawing chamber immediately above the bathsurface, a vertically extending cooling chamber positioned above saiddrawing chamber in communication therewith, means for drawing said glasssheet upwardly through said chambers, a pair of pipes within saiddrawing chamber extending generally horizontally in parallel relation tosaid sheet on the opposite sides thereof and spaced therefrom adjacentthe bath surface, said pipes each having apertures formed in one sidethereof, and means for applying suction to said pipes to draw air fromsaid chamber through said apertures and create a low pressure zone aboutsaid pipes.

5. Apparatus for drawing glass in sheet form from a heated bath ofmolten glass comprising a drawing chamber immediately above the bathsurface, a vertically extending cooling chamber positioned above saiddrawing chamber in communication therewith, cooling means in saiddrawing chamber, means for drawing said glass sheet upwardly throughsaid drawing chamber, a first pair of pipes within said drawing chamberextending generally horizontally in parallel relation to said sheet onopposite sides thereof and spaced therefrom adjacent the bath surface, asecond pair of pipes within said drawing cham ber extending at rightangles to said sheet at the opposite edges thereof and in spacedrelation thereto adjacent the bath surface, said pipes having aperturesformed therein, and means for applying suction to said pipes to draw airfrom said chamber through said apertures and create a low pressure zoneabout said pipes.

References Cited in the tile of this patent UNITED STATES PATENTS1,816,037 Zellers July 28, 1931 2,287,136 Rolland et al. June 23, 19422,693,052 Brchard Nov. 2, 1954

1. A PROCESS FOR THE VERTICAL DRAWING OF GLASS IN SHEET FORM FROM AHEATED BATH OF MOLTEN GLASS INCLUDING DRAWING THE GLASS FROM THE SURFACEOF THE BATH UPWARDLY THROUGH A DRAWING CHAMBER IMMEDIATELY ABOVE SAIDBATH AND SIMULTANEOUSLY WITHDRAWING AIR FROM SAID DRAWING CHAMBER ATPOINTS ADJACENT THE BATH SURFACE AND SPACED FROM THE BASE OF THE GLASSSHEET AT A RATE SUFFICIENT TO MAINTAIN THE PRESSURE IN AN OUTER ZONEADJACENT SAID POINTS AT LEAST AS LOW AS THE PRESSURE IN AN INNER ZONEIMMEDIATELY ADJACENT THE BASE OF THE SHEET TO PREVENT AIR CURRENTSFLOWING TOWARD SAID INNER ZONE FROM SAID OUTER ZONE, SAID ZONES BEING INOPEN COMMUNICATION.
 4. APPARATUS FOR DRAWING GLASS IN SHEET FORM FROM AHEATED BATH OF MOLTEN GLASS COMPRISING A DRAWING CHAMBER IMMEDIATELYABOVE THE BATH SURFACE, A VERTICALLY EXTENDING COOLING CHAMBERPOSITIONED ABOVE SAID DRAWING CHAMBER IN COMMUNICATION THEREWITH, MEANSFOR DRAWING SAID GLASS SHEET UPWARDLY THROUGH SAID CHAMBERS, A PAIR OFPIPES WITHIN SAID DRAWING CHAMBER EXTENDING GENERALLY HORIZONTALLY INPARALLEL RELATION TO SAID SHEET ON THE OPPOSITE SIDES THEREOF AND SPACEDTHEREFROM ADJACENT THE BATH SURFACE, SAID PIPES EACH HAVING APERTURESFORMED IN ONE SIDE THEREOF, AND MEANS FOR APPLYING SUCTION TO SAID PIPESTO DRAW AIR FROM SAID CHAMBER THROUGH SAID APERTURES AND CREATE A LOWPRESSURE ZONE ABOUT SAID PIPES.